Dynamic range is the ratio between the maximum and minimum values of a physical measurement. The dynamic range of real-world scenes can be quite high (i.e., ratios of 100,000:1 are common in the natural world). The human eye is able to perceive such high dynamic ranges in real-world scenes. Dynamic range in an image processing system is considered the ratio between the brightest and darkest parts of a particular scene or picture. For a camera sensor environment, dynamic range is defined as the ratio between the largest possible measurement and the smallest possible measurement the sensor can generate. The largest measurement is limited by the physical pixel well size. The smallest measurement is limited by the physical noise floor. Raw pixel values from a camera sensor are proportional to the amount of light measured. In this sense, raw images from a camera sensor are scene-referred, accurately representing (within the dynamic range capability of the sensor) the original light values captured for the scene. Typical dynamic range for a camera sensor in a conventional consumer device is up to around 1000:1.
There can be a gap of several orders of magnitude in dynamic range difference between human eye perception of a natural scene and what a conventional camera sensor is capable of capturing and representing. Conventional camera images often lack detail in the shadow and/or highlight regions present in natural scenes compared with similar scenes directly perceived by the human eye.
High dynamic range (HDR) imaging is a set of techniques sometimes used in still cameras. Conventional still image sensors can use HDR techniques to form images that show a greater dynamic range of luminance between the lightest and darkest areas when compared with conventional camera photographic approaches. HDR techniques provide images more like what the human eye would see. The HDR process involves combining more than one image captured by a conventional camera sensor of a given scene. Conventional camera sensors can only capture low dynamic range (LDR) or standard dynamic range (SDR) images. HDR techniques produce a final low dynamic range image that shows tonal details of the entire dynamic range captured by the different exposures.
HDR techniques produce a final low dynamic range image as a standard camera image file, typically an 8-bit per color channel RGB image that is JPEG compressed. The final output has limited dynamic range since standard display devices only reproduce a low range (around 100 to 200:1). For paper prints, the range is even lower.
It would be desirable to implement a method and/or apparatus for high dynamic range image processing in a video image processing system.